1. Field of the Invention
The present invention relates to a technology for improving a display performance of a liquid crystal display device employing a vertically aligned mode (VA mode).
2. Background Art
In order to enhance the overall display quality of liquid crystal display devices, it is preferable that neither contrast change nor color change depending upon the viewing direction is observed. In particular, it is important to minimize the color change in the black state depending on the observation direction and to enhance a contrast ratio on the occasion of observation from various directions.
In order to minimize the color change of a liquid crystal display device in the black state when being observed in the oblique direction, there has hitherto been proposed a method of controlling the wavelength dispersion of retardation of an optical film (JP-A-2002-221622). However, following an increase in screen size in recent years, the difference of the display depending on the observation position has been more and more distinguishable, and that problem that the coloration of the display is different between when being observed in the normal direction and in the oblique direction has been recognized.
In order to make the hue observed in the oblique direction closer to the hue observed in the normal direction, there is known a method of adjusting retardation along the thickness direction of a color filter (JP-A-2009-181070). Although, according to this method, the hue change depending on the observation direction becomes small, the display suffers from being bluish as a whole.
On the other hand, in recent years, a high contrast ratio (CR) of a liquid crystal display device is being advanced. In particular, VA-mode liquid crystal display devices have an advantage that CR in the direction normal to a screen (hereinafter referred to as “front CR”) is high as compared with other modes, and researches and developments are made for further improving the advantage. As a result, in these 6 years, the front CR in VA-mode liquid crystal display devices has increased from about 400 to about 8,000, or by about 20 times.
Also, in order to increase a contrast ratio observed in the oblique direction (hereinafter referred to as “viewing angle CR”), there is known a method of controlling a retardation of the optical film (for example, JP-A-2006-184640).
Besides the hue, in order to improve the display quality, increasing a contrast ratio observed in the horizontal direction (hereinafter referred to as “horizontal CR”) is also required.